Caution urged over links in fluoride study
Already there are people who claim fluoridated water is doing bad things to us. Now comes a new study suggesting a link between fluoride exposure in pregnancy and lower IQs in children.
Anti-fluoridation activists are calling it “the biggest moment in the history of this whole debate” and that any government that continues to add fluoride to tap water is condoning “one huge, awful human experiment.”
It’s exactly the response health policy experts — and some of the authors themselves — feared.
“There are some pretty bizarre theories out there, such as the idea that fluoride is being used to sedate the population,” said University of Alberta health policy researcher Tim Caulfield.
“I worry that this study — which the authors note should be replicated, and they call for further analysis and research — will be presented as definitive. It is not.”
In what is being described as the first study of its kind and size exploring fluoride exposure and different stages of brain development, University of Toronto-led researchers analyzed data from 287 mother-child pairs in Mexico City. The study recruited pregnant women from 1994 to 2005, and has followed the women and their children since.
The researchers measured fluoride in archived urine samples taken from the women when they were pregnant, as well as from their children when they were between ages six and 12.
Next they looked at how levels of fluoride in urine related to how children scored on intelligence and neurocognitive function tests when they were four, and again between six and 12.
Children scored 2.5 to three points lower on IQ tests for every 0.5 milligram-perlitre increase in their mother’s urinary fluoride levels beyond 0.8 mg/L.
There was no clear association between IQ scores and values below 0.8 mg/L. As well, the children’s own urinary fluoride levels, measured when they were being tested, didn’t seem to have a significant effect. That suggests that whatever effect fluoride might have on brain development occurs in the womb.
In Canada and the U.S., most fluoride exposure comes from the fluoridation of drinking water to prevent cavities, and fluoride in toothpaste.
In Mexico, “not many people drink tap water,” said Dr. Howard Hu, the study’s principal investigator and founding dean of the University of Toronto’s Dalla Lana School of Public Health. Instead, the women were exposed to fluoridated salt.
The researchers adjusted for numerous “confounders," including the baby’s birth weight, the mother’s smoking history, IQ, socioeconomic status and lead exposure.
The Mexican mothers had, on average, 0.90 milligrams per litre of fluoride in their stored urine, which the researchers said is in the “general range of exposures” reported for other populations.
According to Hu, one 2012-2013 survey showed the mean urinary fluoride levels for Canadians were about 0.43 milligrams per litre, about half the Mexican levels.
Still, “the urinary fluoride levels of these (Mexican) women were definitely not sky high,” Hu said.
However, the findings may mean that "there still may be a level of fluoride exposure among both pregnant women and everybody else that can still preserve the beneficial effects on tooth decay, while avoiding any effects on intelligence,” Hu said.
The team cautions their findings need to be confirmed in other populations. And Hu said it’s hard to make direct comparisons with women in the U.S. or Canada, where there haven’t been large population studies of maternal urinary fluoride levels.
But he said the study raises a red flag. “This is a very rigorous epidemiology study. You just can’t deny it. It’s directly related to whether fluoride is a risk for the neurodevelopment of children. So, to say it has no relevance to the folks in the U.S. seems disingenuous.”
In a statement, the American Dental Association said the findings “are not applicable” to the U.S. “Because it’s not known how the subjects of the study ingested the fluoride — whether through salt, water or both — no conclusions can be drawn regarding the effects of community water fluoridation in the U.S.”
Across Canada, numerous cities like Ottawa, Edmonton and Toronto still fluoridate their water. Others like Calgary, Waterloo and Windsor have been taking it out.
Opponents claim fluoridation causes, among other things, heart disease, cancer, birth defects, kidney problems, goiters, ulcers, anemia and spontaneous abortion. “However, these associations are not supported by the scientific literature,” University of Guelph researchers wrote in a 2014 evidence review for the National Collaborating Centre for Environmental Health.